A laminated circuit board with electronic components buried therein will be described with reference to FIG. 67. Laminated circuit board 670 with electronic components buried therein is such that substrates 2a to 2e formed from thermoplastic resin are laminated on one main surface of substrate 1 formed of a metallic base member.
The words “one main surface” and “the other main surface” used in the following description respectively stand for one surface in the direction of thickness and the opposite side surface in those being relatively less in thickness than the sizes of length and width such as resin boards or various sheets. Accordingly, the word “one main surface” does not mean only a “surface” of a resin board or sheet, and the word “the other main surface” does not mean only a “back” of a resin board or sheet.
In FIG. 67, hole 4 for burying electronic component 3 therein is formed in substrate 2c, 2d. Pattern 5 is provided on one main surface or the other main surface of substrates 2a to 2e. Conductive paste 6 is filled into via-hole 7 formed in substrates 2a to 2e. Electrode 8 is provided at both ends of electronic component 3, and it is conducting with conductive paste 6.
Here, conductive paste 6 includes tin particles and silver particles. Also, for precisely aligning electrode 8 to via-hole 7 filled with conductive paste 6, the clearance between hole 4 and electronic component 3 is 20 μm over the entire periphery of electronic component 3, which is nearly the same in size as the outside dimension of electronic component 3.
A laminated circuit board having such a configuration is heated under pressure at temperature 250° C. to 350° C. and pressure 1 to 10 MPa for 10 to 20 minutes to complete laminated circuit board 670. As it is heated under pressure in this way, tin is melted and integrated with silver, and electrode 8 of electronic component 3 is connected to conductive paste 6, then electronic component 3 is electrically and mechanically fixed on laminated circuit board 670.
As prior art documents related to this kind of technology, for example, a patent is disclosed in the publication of Japanese Patent Laid-Open Application No. 2003-86949.
However, in such a conventional laminated circuit board 670 with electronic component 3 buried therein, as the mounting density of electronic component 3 is increased, there arises the following problem. That is, as shown in FIG. 68, for example, if electronic components 3a to 3e are mounted on substrate 2c with narrow pitch 9 of 100 μm, as in FIG. 69 showing the cross-section, width 11 of crosspiece 10a disposed between electronic components 3a and 3b is 60 μm (100 μm−20 μm×2). On the other hand, thickness 12 of substrate 2c is 75 μm, and width 11 of crosspiece 10a is less in thickness than substrate 2c. Therefore, it is physically difficult to manufacture laminated circuit board 670.
As shown in the plan view of electronic components 3 (3a to 3e) in FIG. 70 and the sectional view of electronic components 3 (3a to 3e) in FIG. 71, it can be considered that there is provided hole 13 including electronic components 3a to 3e mounted with narrow pitch 9. However, since substrate 2c is thermoplastic, for example, resin 15 is not sufficiently filled between electronic components 3a and 3b, causing air 16 to remain therein.
After that, if circuit board 670 is subjected to reflow soldering, air 16 is expanded due to the reflow temperature, causing a great stress to be applied between electronic component 3a and electronic component 3b. 
A great stress then applied is the cause of a problem such that the connection of electronic components 3 is affected. That is, the conduction of conductive paste 6 shown in FIG. 67 is cut off or cracking takes place after resin sealing, and water intrudes through such crack causing electrode 8 to get rusted, which leads to defective insulation.
On the other hand, it can be considered that the heat fluidity of resin is increased for enhancing the filling efficiency of resin. However, in this case, there is a problem that the shape of thermoplastic substrate 2c itself cannot be maintained.